EMULATING AN OPERATING SYSTEM ON TOP OF ANOTHER

In this paper, we present the design of an operating-system emulator. This software interface provides the services of one operating system (Oberon) on a machine running a different operating system (Macintosh), by mapping the functions of the first onto equivalent calls to the second. The construction of this emulator proceeded in four distinct phases, documented here through examples from each of these phases. We believe that our four-phase approach can be beneficial whenever a larger software system needs to be adapted from one architecture onto another. In conclusion, we relate some of the lessons learned and propose guidelines for similar engineering projects.